Method for production of a radiation-emitting semiconductor chip

ABSTRACT

A method for micropatterning a radiation-emitting surface of a semiconductor layer sequence for a thin-film light-emitting diode chip. The semiconductor layer sequence is grown on a substrate. A mirror layer is formed or applied on the semiconductor layer sequence, which reflects back into the semiconductor layer sequence at least part of a radiation that is generated in the semiconductor layer sequence during the operation thereof and is directed toward the mirror layer. The semiconductor layer sequence is separated from the substrate by means of a lift-off method, in which a separation zone in the semiconductor layer sequence is at least partly decomposed in such a way that anisotropic residues of a constituent of the separation zone, in particular a metallic constituent of the separation layer, remain at the separation surface of the semiconductor layer sequence, from which the substrate is separated. The separation surface—provided with the residues—of the semiconductor layer sequence with a dry etching method, a gaseous etchant or a wet-chemical etchant, wherein the anisotropic residues are at least temporarily used as an etching mask. A semiconductor chip is produced according to such a method.

RELATED APPLICATIONS

This is a U.S. national stage of application No. PCT/DE2004/000892,filed on 29 Apr. 2004.

FIELD OF THE INVENTION

The invention lies in the field of the micropatterning ofradiation-emitting semiconductor chips. It relates to the roughening ofa radiation-emitting surface of a radiation-generating semiconductorlayer sequence, in particular a radiation coupling-out surface of aradiation-emitting semiconductor layer sequence of a thin-film lightemitting diode chip.

BACKGROUND OF THE INVENTION

A thin-film light emitting diode chip is distinguished in particular bythe following characteristic features:

-   -   a reflective layer is applied or formed at a first main        surface—facing toward a carrier element—of its        radiation-generating epitaxial layer sequence, which reflective        layer reflects at least part of the electromagnetic radiation        generated in the epitaxial layer sequence back into the latter;    -   the epitaxial layer sequence has a thickness in the region of 20        μm or less, in particular in the region of 10 μm; and    -   at a second main surface—remote from the reflective layer—of the        radiation-generating epitaxial layer sequence, the latter has an        intermixing structure which ideally leads to an approximately        ergodic distribution of the light in the epitaxial layer        sequence, that is to say that it has an as far as possible        ergodically stochastic scattering behavior.

A basic principle of a thin-film light emitting diode chip is describedfor example in I. Schnitzer et al., Appl. Phys. Lett. 63 (16), Oct. 18,1993, 2174-2176, the disclosure content of which is in this respecthereby incorporated by reference.

The emitting zone of a thin-film light emitting diode chip isessentially restricted to the front-side patterned coupling-out surfaceof the extremely thin epitaxial layer sequence, as a result of whichvirtually the conditions of a Lambert surface radiator are established.

SUMMARY OF THE INVENTION

One object of the present invention is to provide an improved method forproducing a micropatterning and also a thin-film light emitting diodechip having improved coupling out of light.

This and other objects are attained in accordance with one aspect of theinvention directed to a method for micropatterning a radiation-emittingsurface of a semiconductor layer sequence for a thin-film light-emittingdiode chip comprising the steps of (a) growing the semiconductor layersequence on a substrate, (b) forming or applying a mirror layer on thesemiconductor layer sequence, which reflects back into the semiconductorlayer sequence at least part of a radiation that is generated in thesemiconductor layer sequence during operation thereof and is directedtoward the mirror layer, (c) separating the semiconductor layer sequencefrom the substrate with a lift-off method, in which a separation zone inthe semiconductor layer sequence is at least partly decomposed in such away that anisotropic residues of a constituent of the separation zoneremain at a separation surface of the semiconductor layer sequence, fromwhich the substrate is separated, and (d) etching the separationsurface—provided with the residues—of the semiconductor layer sequencewith a dry etching method, a gaseous etchant or a wet-chemical etchant,wherein the residues are at least temporarily used as an etching mask.

Another aspect of the present invention is directed to a method formicropatterning a radiation-emitting surface of a semiconductor layersequence for a thin-film light-emitting diode chip comprising the stepsof (a) growing the semiconductor layer sequence on a substrate, (b)forming or applying a mirror layer on the semiconductor layer sequence,which reflects back into the semiconductor layer sequence at least partof a radiation that is generated in the semiconductor layer sequenceduring the operation thereof and is directed toward the mirror layer,(c) separating the semiconductor layer sequence from the substrate,wherein a separation zone made of compound semiconductor material of thesemiconductor layer sequence is at least partly decomposed, and (d)etching a separation surface of the semiconductor layer sequence, fromwhich the substrate is separated, by means of an etchant whichpredominantly etches at crystal defects and selectively etches differentcrystal facets at the separation surface.

Another aspect of the invention is directed to anelectromagnetic-radiation-emitting semiconductor chip comprising: anepitaxially produced semiconductor layer sequence having an n-conductingsemiconductor layer, a p-conducting semiconductor layer and anelectromagnetic-radiation-generating region arranged between these twosemiconductor layers, at least one of the semiconductor layers having anitride compound semiconductor material, and a carrier body, on whichthe semiconductor layer stack is arranged, wherein at least onesemiconductor layer of the semiconductor layer sequence ismicropatterned by means of a method as described above.

A method according to the technical teaching on which the presentinvention is based is particularly preferably suitable for thin-filmlight emitting diode chips having an epitaxial layer sequence based onnitride compound semiconductor material, in particular based onsemiconductor material from the nitride compound semiconductor materialsystem In_(x)Al_(y)Ga_(1-x-y)N where 0≦x≦1, 0≦y≦1 and x+y≦1.

In the present case, the group of semiconductor layer sequences based onnitride compound semiconductor material includes, in particular, thosesemiconductor layer sequences in which the epitaxially producedsemiconductor layer which generally has a layer sequence made ofdifferent individual layers contains at least one individual layer whichcomprises a material from the nitride compound semiconductor materialsystem In_(x)Al_(y)Ga_(1-x-y)N where 0≦x≦1, 0≦y≦1 and x+y≦1.

Such a semiconductor layer sequence may have for example a conventionalpn junction, a double heterostructure, a single quantum well structure(SQW structure) or a multiple quantum well structure (MQW structure).Such structures are known to the person skilled in the art and aretherefore not explained in any further detail at this juncture. Oneexample of a multiple quantum well structure based on GaN is describedin U.S. Pat. No. 6,849,881, the disclosure content of which is herebyincorporated by reference.

A method for micropatteming a radiation-emitting surface of asemiconductor layer sequence for a thin-film light emitting diode chipaccording to an embodiment of the invention is based on the basicconcept that after the epitaxial growth of the semiconductor layersequence on a growth substrate optimized to the greatest possible extentwith regard to the growth conditions and after the formation orapplication of the mirror layer onto the semiconductor layer sequencethe semiconductor layer sequence is separated from the growth substrate.This separation is effected in a separation zone of the semiconductorlayer sequence, which is at least partly decomposed in such a way thatanisotropic residues of a constituent of the separation zone, inparticular a metallic constituent of the separation layer, remain at theseparation surface of the semiconductor layer sequence, from which thesubstrate is separated.

The separation surface of the semiconductor layer sequence, on which theresidues are situated, is subsequently etched in material-removingfashion during a preliminary etching step using the residues as anetching mask by means of a dry etching method, by means of a gaseousetchant or by means of a wet-chemical etchant. In this case, theresidues are preferably simultaneously eliminated at least for the mostpart, that is to say that the anisotropic residues act only temporarilyas an etching mask.

The residues remain after the separation step on the separation surfaceusually as a continuous layer having a varying thickness or already haveinsular or reticulated zones with interspaces in which the surface ofthe semiconductor layer sequence has already been uncovered.

During the preliminary etching step, the semiconductor layer sequence isthen etched to different extents depending on the layer thickness of theresidues, with the result that a roughening of the separation surface ofthe semiconductor layer sequence arises.

In one preferred embodiment, different crystal facets of thesemiconductor layer sequence are uncovered. After the preliminaryetching of the separation surface, the latter is particularlyadvantageously treated by means of a subsequent etching step with awet-chemical or gaseous etchant which predominantly etches at crystaldefects and selectively etches different crystal facets at theseparation surface of the semiconductor layer sequence. For thispurpose, the wet-chemical etchant particularly preferably contains KOH.A corrosive gas such as H or Cl, for example, is suitable as the gaseousetchant. H is preferably used as an etching gas at an elevatedtemperature, in particular greater than or equal to 800° C.

For the case where during the separation of the semiconductor layersequence from the growth substrate, only insignificant residues remainon the separation surface and/or these can be eliminated at least forthe most part by means of an etchant which predominantly etches atcrystal defects of the semiconductor layer sequence and selectivelyetches different crystal facets at the separation surface, thepreliminary etching step set forth above may be obviated.

In the case of a separation zone with nitride compound semiconductormaterial, this zone is preferably decomposed in such a way that gaseousnitrogen arises. For this purpose, a laser lift-off method (also calledlaser lift-off for short) is particularly preferably suitable asseparation method. Such a laser lift-off method is explained inpublished U.S. patent application U.S. 2004/0072382 for example, thedisclosure content of which is hereby incorporated by reference. Adifferent separation method in which anisotropic residues of aconstituent of the separation layer, in particular a metallicconstituent of the separation layer, remain at the separation surfacecould be used as an alternative.

The semiconductor layer sequence advantageously has at the separationsurface an increased defect density in comparison with a part of thesemiconductor layer sequence that is disposed downstream of theseparation surface from the point of view of the substrate. Theseparation zone preferably lies in a buffer layer between growthsubstrate and radiation-generating region of the semiconductor layersequence.

A buffer layer is a semiconductor layer of the semiconductor layersequence which faces toward the substrate and which essentially servesfor producing an optimum growth surface for the subsequent growth of thefunctional layers of the semiconductor layer sequence (for example amultiple quantum well structure). Such a buffer layer compensates forexample for differences between the lattice constant of the substrateand the lattice constant of the semiconductor layer sequence and alsocrystal defects of the substrate. The buffer layer can likewise be usedto set strain states for the growth of the semiconductor layer sequencein a targeted manner.

Particularly preferably, the separation zone substantially has GaN andpreferably anisotropic residues made of metallic Ga remain on theseparation surface of the semiconductor layer sequence.

That region of the semiconductor layer sequence in which the separationzone is situated is preferably provided with a dopant concentration ofbetween 1*10¹⁸ cm⁻³ and 1*10¹⁹ cm⁻³ inclusive. In this case, thesemiconductor layer sequence advantageously has a dopant concentrationof between 1*10¹⁸ cm⁻³ and 1*10²⁰ cm⁻³ inclusive at its separationsurface. This simplifies the formation of an ohmic contact on thesemiconductor layer sequence. If the region is substantially based onGaN, then Si is preferably used as the dopant.

In another preferred embodiment, the separation zone contains AlGaN, theAl content of which is chosen in such a way that it is decomposed duringthe separation of the semiconductor layer sequence from the growthsubstrate, and Al is sintered into the semiconductor layer sequence. Forthis purpose, the Al content preferably lies between approximately 1%and approximately 10%, in particular between approximately 1% andapproximately 7%. In order to produce an Al-n-type contact, during theseparation operation Al is preferably melted and sintered into thesemiconductor layer sequence. For this purpose, a laser lift-off methodis particularly preferably used in which the laser has a wavelength in arange of less than 360 nm, preferably a wavelength of between 350 nm and355 nm inclusive.

In one advantageous development of the method, the separation zone has aGaN layer adjoined by an AlGaN layer as seen from the substrate. Duringthe separation of the semiconductor layer sequence from the growthsubstrate, the entire GaN layer and part of the AlGaN layer aredecomposed. This entails the advantage that if it is necessary forreasons of layer quality or for other reasons, firstly it is possible togrow a GaN layer which is thinner than the separation zone which isdecomposed during the separation operation. During the separationoperation, the GaN layer and part of the overlying AlGaN layer are thendecomposed, which, if desired, is associated with the advantagesoutlined in the previous paragraph. The AlGaN layer in this case onceagain preferably has an Al content that lies between approximately 1%and approximately 10%, in particular between approximately 1% andapproximately 7%.

A sapphire substrate is preferably used as the growth substrate. Thisadvantageously has good transmissivity in a large wavelength range forelectromagnetic radiation. In particular, sapphire is transmissive forwavelengths of less than 350 nm, which is of great importance withregard to the decomposition of GaN or GaN-based material.

In a further method step, a contact pad, in particular a contactmetallization for electrical connection of the semiconductor layersequence, is applied to the micropatterned separation surface of thesemiconductor layer sequence. The conventionally known metallizationlayers, such as, for example TiAl, Al or TiAlNiAu contacts, are suitablefor this purpose.

Particularly preferably, through the micropatterning at the separationsurface of the semiconductor layer sequence a roughening is produced ona scale (that is to say with a feature size) which corresponds to awavelength range (relative to the internal wavelength in the chip) of anelectromagnetic radiation generated by the semiconductor layer sequenceduring operation thereof.

The method is particularly preferably applied in the case of asemiconductor layer sequence based on semiconductor material from thehexagonal nitride compound semiconductor material systemIn_(x)Al_(y)Ga_(1-x-y)N where 0≦x≦1, 0≦y≦1 and x+y≦1, in which the 000-1crystal face (n face of the hexagonal nitride lattice) faces toward thegrowth substrate.

The epitaxial growth of the semiconductor layer sequence is preferablyeffected by means of MOVPE (metal organic vapor phase epitaxy).

A Bragg mirror may be applied as the mirror layer. As an alternative, itis possible to produce a mirror layer having a radiation-transmissivelayer and a reflective layer disposed downstream thereof as seen fromthe semiconductor layer sequence.

It is likewise possible for the mirror layer to have a reflection layerwith a plurality of windows toward the semiconductor layer sequence andfor a current transport layer that is different from the reflectionlayer to be arranged in the windows.

An electromagnetic-radiation-emitting semiconductor chip produced by amethod according to the invention has at least one epitaxially producedsemiconductor layer sequence having an n-conducting semiconductor layer,a p-conducting semiconductor layer and anelectromagnetic-radiation-generating region arranged between these twosemiconductor layers. At least one of the semiconductor layers containsa nitride compound semiconductor material and the semiconductor layersequence is mounted onto a carrier body by that side which is remotefrom a micropatterned surface of the semiconductor layer sequence, thatis to say by the side on which the mirror is arranged. In a furtherembodiment of the semiconductor chip, the mirror layer is alsomicropatterned.

In one embodiment of the method, after the lift-off step by means oflaser lift-off, for example, only a reticulated or insular structure ofmetallic material remains rather than a completely continuous layer ofmetallic material from the separation zone on the semiconductor layersequence, which structure, during the subsequent preliminary etchingstep, is transferred at least approximately into the semiconductor layersequence in order to deliberately offer different crystal facets for thesubsequent etching step. During the subsequent etching step, the etchantacts selectively on different crystal facets and thus leads to amicroscopic roughening of the separation surface of the semiconductorlayer sequence. Etching edges from the preliminary etching step andcrystal defects in the semiconductor layer sequence at the separationsurface thereof serve as etching seeds in this case.

The formation or the application of the mirror layer on thesemiconductor layer sequence, which reflects back into the semiconductorlayer sequence at least part of a radiation generated in thesemiconductor layer sequence during the operation thereof, may beeffected before or after the micropatterning of the semiconductor layersequence, the former alternative being particularly preferred. Themirror layer represents an essential constituent of a thin-film lightemitting diode. The mirror layer may also be connected to themicropatterned semiconductor layer sequence together with a carrier bodyfor the semiconductor layer sequence.

In principle, the invention is not restricted to use in the case of athin-film light emitting diode chip, but rather can be used in principlewherever micropatterned surfaces are required on epitaxially producedsemiconductor layer sequences stripped from the growth substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a to 1 e show a schematic illustration of a method sequence inaccordance with a first exemplary embodiment,

FIGS. 2 a and 2 b show SEM micrographs of a semiconductor surface atdifferent method stages of the exemplary embodiment, and

FIGS. 3 a to 3 e show a schematic illustration of a method sequence inaccordance with a second exemplary embodiment.

DETAILED DESCRIPTION OF THE DRAWINGS

In the exemplary embodiments and figures, identical or identicallyacting constituents are in each case provided with the same referencesymbols. The layer thicknesses illustrated are not to be regarded astrue to scale, rather they are illustrated with exaggerated thicknessesin order to afford a better understanding. The epitaxial layers, too,are not illustrated with the correct thickness relationships with oneanother.

In the method sequence illustrated schematically in FIGS. 1 a to 1 e,firstly a semiconductor layer sequence is grown onto a growth substrate1 made of sapphire by means of metal organic vapor phase epitaxy(MOVPE). Said semiconductor layer sequence has, proceeding from thesapphire substrate 1, the following successive layers (cf. FIG. 1 a):

-   -   Si-doped GaN buffer layer 2    -   Si-doped GaN contact layer 3 (may also belong in part to the        buffer layer)    -   Si-doped GaN cap layer 4    -   Layer 5 that generates electromagnetic radiation (in particular        green or blue light) and has a multiple quantum well structure        with a plurality of InGaN quantum wells and GaN barriers        situated between the latter    -   p-doped AlGaN cap layer 6 (e.g. Mg as p-type dopant).

Although not shown, the p-doped AlGaN cap layer 6 is preferably alsofollowed by a p-doped GaN layer (for example likewise doped with Mg).

The contact layer 3 may alternatively have Si:AlGaN.

A multiple quantum well structure mentioned above is described in U.S.Pat. No. 6,849,881 for example, the disclosure content of which ishereby incorporated by reference.

A single quantum well structure, a double heterostructure or a singleheterostructure may also be used instead of the multiple quantum wellstructure.

A metallic mirror layer 7 is applied on the semiconductor layer sequence100, said mirror layer being designed in such a way that it can reflectan electromagnetic radiation generated in the active layer back into thesemiconductor layer sequence 100. Al or Ag is suitable as mirrormaterial in the blue spectral range. With the use of Ag, the mirrorlayer may be underlaid with a thin Ti, Pd or Pt layer. This leads inparticular to an improved adhesion of the Ag layer on the semiconductorlayer sequence 100. The layer thickness of such an adhesion improvinglayer is preferably less than 1 nm.

As an alternative, a Bragg mirror may be applied as the mirror layer 7or it is possible to produce a mirror layer which has aradiation-transmissive layer, e.g. made of ITO, and a reflective layerdisposed downstream thereof as seen from the semiconductor layersequence. It is likewise possible for the mirror layer to have areflection layer with a plurality of windows toward the semiconductorlayer sequence 100 and for a current transport layer that is differentfrom the reflection layer to be arranged in the windows.

The semiconductor layer sequence is subsequently connected by the mirrorside to an electrically conductive carrier body 10, which is made forexample of GaAs, Ge or Mo. This is effected for example by means ofeutectic bonding by means of AuGe, AuSn or PdIn. However, soldering oradhesive bonding is possible, too. The sapphire substrate 1 issubsequently separated by means of a laser lift-off method indicated bythe arrows 110 in FIG. 1 b, the buffer layer 2 being decomposed in sucha way that gaseous nitrogen arises and residues 20 made of metallicgallium remain in the form of an anisotropic layer having a varyinglayer thickness on the semiconductor layer sequence 100. In thisrespect, cf. FIG. 1 c. A corresponding laser lift-off method isdescribed in U.S. published patent application U.S. 2004/0072382, forexample, the disclosure content of which is hereby incorporated byreference.

The residues 20 are subsequently removed during a preliminary etchingstep using an etchant 120 which etches in material-removing fashion bothmetallic Ga and the Si-doped GaN contact layer 3. The surface of theSi-doped GaN contact layer 3 is thereby roughened. In this case, theanisotropically distributed residues made of metallic gallium act as atemporary etching mask in this respect.

Wet-chemical etching is preferably effected during the preliminaryetching step. In particular, KOH in dilute form is suitable as theetchant. In a particularly preferred configuration of the invention, KOHwith a concentration of 5% at room temperature is used during thisetching step, the etching duration being between 5 min and 15 min.

As an alternative, for example a dry etching method (RIE method) is alsosuitable for the preliminary etching step. A dry etching methodgenerally acts in a directional manner, so that in this configuration ofthe invention the form of the residues is transferred into theunderlying semiconductor layer and a roughening of said semiconductorlayer is thus obtained.

In a further alternative of the invention, a corrosive gas, for exampleH or Cl, is used as the etchant, preferably at an elevated temperaturethat is, in particular, greater than or equal to 800° C.

The laser lift-off methods comprise a decomposition of semiconductormaterial. The space being filled with the material that is to bedecomposed is defined as the “separation zone”. According to oneembodiment, the separation zone is equal to the buffer layer, i.e. thethickness and the position of the separation zone and of the bufferlayer are substantially identical. According to another embodiment, theseparation zone comprises a thickness which is thinner than the bufferlayer's thickness. As one example of this embodiment, the separationzone is a part of the buffer layer. As another example, the separationzone overlaps partly with the buffer layer. As yet another example, theseparation zone is spaced by a short distance from the buffer layer.

Different crystal facets of the contact layer 3 are uncovered during thepreliminary etching step. The preliminarily etched surface of thecontact layer 3 is then treated with a further wet-chemical etchant in asubsequent etching step (indicated by the arrows having the referencesymbol 130), which etchant predominantly etches at crystal defects andselectively etches different crystal facets at the separation surface ofthe semiconductor layer sequence (cf. FIG. 1 d). The furtherwet-chemical etchant contains KOH in the case of the example. Thesurface of the contact layer can be roughened very effectively by thetreatment with KOH; the roughness produced during the preliminaryetching is considerably improved with regard to efficiency for couplingout radiation.

KOH in concentrated form is preferably used as the etchant during thesubsequent etching step. In a further preferred configuration of theinvention, etching is in this case effected using KOH having aconcentration of 25% at a temperature of between 70° C. and 90° C., forexample at 80° C., the etching time being between 3 min and 10 min.

As an alternative, a corrosive gas, for example H or Cl, may be used asthe etchant for the subsequent etching step.

FIG. 2 a shows a surface after the dry etching used for the preliminaryetching step. FIG. 2 b shows a surface after the further etching usingKOH.

To improve the roughening effect, the contact layer 3 has, at least atthe side facing toward the buffer layer 2, an increased defect densityin comparison with the subsequent layers 4, 5 and 6. It is usuallydesirable to realize as low a defect density as possible. However, inaccordance with an embodiment of the invention, it is taught todeliberately significantly increase the defect density of one of thesemiconductor layers as compared to the usually sought after low defectdensity in order to improve the roughening effect. The higher the defectdensity, the more disorder there is in the semiconductor layer, which ishelpful for realizing a rough (“disordered”) surface as compared to asmooth (“ordered”) surface.

Furthermore, the contact layer 3 has an Si dopant concentration ofbetween 1*10¹⁸ cm⁻³ and 1*10¹⁹ cm⁻³ inclusive at least at the sidefacing toward the buffer layer. This enables simple production of anohmic contact on the contact layer 3.

In an alternative configuration of the exemplary embodiment, the GaNbuffer layer 2 is thinner than the layer thickness decomposed during thelaser lift-off method, and the Al content of the contact layer 3 isbetween approximately 1% and approximately 7% at least in a regionfacing toward the buffer layer 2. Said region of the contact layer 3 isdecomposed with the formation of gaseous nitrogen and metallic Ga and Alduring laser lift-off and Al is melted and sintered into the remainingcontact layer 3. This is shown in FIG. 1 d.

An aluminum n-type contact can be produced at the GaN contact layer 3 inthis way.

A bonding pad, in particular a bonding pad metallization for theelectrical connection of the n-type side of the semiconductor layersequence 100, is subsequently applied to the micropatterned surface ofthe GaN contact layer 3 (FIG. 1 e). Said bonding pad has TiAl, forexample.

The micropatterning of the contact layer 3 produces a roughening on ascale corresponding to the blue spectral range of the visible spectrumof electromagnetic radiation. The roughening structures are, inparticular, of the order of magnitude of half an internal wavelength ofthe electromagnetic radiation generated in the active semiconductorlayer 5.

During the growth of the epitaxial layer sequence by means of MOVPE(metal organic vapor phase epitaxy), the 000-1 crystal face (N face ofthe hexagonal nitride lattice) preferably faces toward the sapphiregrowth substrate.

A laser radiation source having a wavelength in the range of between 350nm and 360 nm or with a shorter wavelength is used as the radiationsource for the laser lift-off method.

On that side of the carrier body 10 which is remote from thesemiconductor layer sequence 100, before or after said carrier body isconnected to the semiconductor layer sequence 100, there is applied acontact layer 12 for the electrical connection of the thin-film lightemitting diode chip 20, said chip being illustrated in FIG. 1 e, suchFIG. 1 e showing only a part of the chip 20 (because a part of layer 10is omitted). Said contact layer comprises Al or a Ti/Al layer sequence,by way of example.

In a further embodiment of the method, the mirror layer may bemicropatterned with a similar scale to the contact layer 3 prior to theconnection to the carrier body 10.

In an alternative configuration of the method according to the exemplaryembodiment, after laser lift-off, only a reticulated or insularstructure of metallic Ga and, if appropriate, Al residues remains ratherthan a completely continuous layer of metallic Ga and, if appropriate,Al on the contact layer 3, which structure, during the subsequentpreliminary etching step, is at least approximately transferred into thecontact layer 3 in order to deliberately offer different crystal facetsfor the subsequent KOH etch.

What is suitable for the preliminary etching step is once again, asdescribed above, a dry etching method (RIE method) or a wet-chemicaletching method, preferably using KOH in dilute form (e.g. KOH 5% at roomtemperature; etching time 5 min to 15 min).

For the subsequent etching step that follows, once again use ispreferably made of KOH, particularly preferably in concentrated form asdescribed above.

KOH acts selectively on different crystal facets and thus leads to amicroscopic roughening. In this case, etching edges from the precedingRIE process and crystal defects in the contact layer or, if appropriate,in the residual region of the buffer layer 2, if the latter has not beencompletely decomposed during laser lift-off, serve as etching seeds.

As an alternative, a corrosive gas, for example H or Cl, may once againbe used as the etchant for the subsequent etching step, preferably at anelevated temperature that is, in particular, greater than or equal to800° C.

The exemplary embodiment illustrated schematically in FIGS. 3 a to 3 ediffers from that in FIGS. 1 a to 1 e and the various embodimentsthereof in particular by the fact that virtually no or no residues atall of metallic Ga and, if appropriate, Al remain on the contact layer 3during laser lift-off 110 (FIG. 3 b), and that directly after laserlift-off 110, the contact layer 3 is etched (indicated by the arrows 130in FIG. 3 c) with a KOH-containing etchant, preferably in theconcentrated form described above.

It goes without saying that in this case, too, it is possible, ifexpedient, to effect preliminary etching before the etching with KOH inorder, for example, to uncover different crystal facets and/or defects,or it is possible, as described, to use a corrosive gas such as H or Clas the etchant.

As an alternative, it is also possible in this case, in the same way asin the exemplary embodiment described above in conjunction with FIGS. 1a to 1 e, for a residual layer of the buffer layer 2 to remain on thecontact layer after separation from the substrate 1 if said buffer layeris thicker than its zone decomposed during the separation step. Theroughening is then produced on the remainder of the buffer layer 2.

It goes without saying that the above explanation for the invention onthe basis of the exemplary embodiments is not to be understood as arestriction of the invention to these exemplary embodiments. Rather, inparticular all methods in which a separation surface of a semiconductorlayer, after the material-decomposing lift-off thereof from the growthsubstrate, is micropatterned by means of a defect etch come under thebasic concept of the invention.

The scope of protection of the invention is not limited to the examplesgiven hereinabove. The invention is embodied in each novelcharacteristic and each combination of characteristics, which includesevery combination of any features which are stated in the claims, evenif this combination of features is not explicitly stated in the claims.

1. A method for micropatterning a radiation-emitting surface of asemiconductor layer sequence for a thin-film light-emitting diode chip,comprising the steps of: (a) growing the semiconductor layer sequence ona substrate; (b) forming or applying a mirror layer on the semiconductorlayer sequence, which reflects back into the semiconductor layersequence at least part of a radiation that is generated in thesemiconductor layer sequence during operation thereof; (c) separatingthe semiconductor layer sequence from the substrate with a lift-offmethod, in which a separation zone in the semiconductor layer sequenceis at least partly decomposed such that anisotropic residues of aconstituent of the separation zone remain at a separation surface of thesemiconductor layer sequence and the substrate is separated from saidsemiconductor layer sequence, the anisotropic residues being formed onthe semiconductor sequence as a layer having a varying layer thickness;and (d) etching the separation surface—provided with the anisotropicresidues—of the semiconductor layer sequence with a dry etching method,a gaseous etchant or a wet-chemical etchant, wherein the anisotropicresidues are temporarily used as an etching mask, wherein the etchingresults in roughening the separation surface wherein the separation zonethat is decomposed in step (c) contains AlGaN, an Al content of theAlGaN lies between approximately 1% and approximately 10%, and Al ofsaid AlGaN is sintered into the semiconductor layer sequence.
 2. Themethod as claimed in claim 1, wherein in step (d) both anisotropicresidues of the separation zone and the semiconductor layer sequence areetched in material-removing fashion at the separation surface thereof.3. The method as claimed in claim 1, wherein in step (d) differentcrystal facets of the semiconductor layer sequence are uncovered.
 4. Themethod as claimed in claim 1, wherein the wet-chemical etchant containsKOH, or the gaseous etchant contains a corrosive gas.
 5. The method asclaimed in claim 1, wherein after method step (d) the etched separationsurface is treated with a further wet-chemical or gaseous etchant whichpredominantly etches at crystal defects and selectively etches differentcrystal facets at the separation surface of the semiconductor layersequence.
 6. The method as claimed in claim 5, wherein the furtherwet-chemical etchant contains KOH, or the gaseous etchant contains acorrosive gas.
 7. The method as claimed in claim 1, wherein thesemiconductor layer sequence is a radiation-emitting semiconductor layersequence based on nitride compound semiconductor material, and whereinin step (c) nitride compound semiconductor material of the semiconductorlayer sequence is decomposed in the separation zone in such a way thatgaseous nitrogen arises.
 8. The method as claimed in claim 7, wherein alaser radiation source having a wavelength in a range of between 350 nmand 360 nm or a shorter wavelength is used in step (c).
 9. The method asclaimed in claim 1, wherein the lift-off method is a laser lift-offmethod.
 10. The method as claimed in claim 1, wherein the semiconductorlayer sequence has an increased defect density at the separationsurface, as compared with a defect density of a part of thesemiconductor layer sequence that is disposed farther away from thesubstrate than is the separation surface.
 11. The method as claimed inclaim 10, wherein the region of the semiconductor layer sequence inwhich the separation zone is situated is a buffer layer.
 12. The methodas claimed in claim 1, wherein the semiconductor layer sequence containsat least one material from the system In_(x)Al_(y)Ga_(1-x-y)N where 0 ≦x≦1, 0≦y ≦1 and x+y ≦1.
 13. The method as claimed in claim 1, wherein thesemiconductor layer sequence contains at least one material from thesystem In_(x)Al_(y)Ga_(1-x-y)N where 0 ≦x ≦1, 0 ≦y ≦1 and x+y ≦1, andwherein the separation zone substantially has GaN and the anisotropicresidues are made of metallic Ga and remain on the separation surface ofthe semiconductor layer sequence.
 14. The method as claimed in claim 1,wherein the semiconductor layer sequence has a dopant concentration ofbetween 1×10¹⁸cm⁻³ and 1×10²⁰ cm⁻³, inclusive, at its separationsurface.
 15. The method as claimed in claim 14, wherein the dopant isSi.
 16. The method as claimed in claim 1, wherein an aluminum n-contactis produced at the separation surface of the semiconductor layersequence.
 17. The method as claimed in claim 1, wherein a sapphiresubstrate is used.
 18. The method as claimed in claim 1, wherein acontact pad comprising a contact metallization for electrical connectionof the semiconductor layer sequence, is applied to a micropatternedseparation surface of the semiconductor layer sequence.
 19. The methodas claimed in claim 18, wherein through the micropatterning at theseparation surface of the semiconductor layer sequence a roughening isproduced on a scale which corresponds to a wavelength range of anelectromagnetic radiation emitted by the semiconductor layer sequenceduring operation thereof, wherein roughening structures are of an orderof magnitude of half an internal wavelength which is the wavelength ofelectromagnetic radiation generated within the semiconductor layersequence.
 20. The method as claimed in claim 1, wherein thesemiconductor layer sequence is grown overall from hexagonal GaN-basedmaterial on the substrate, wherein a 000-1 crystal face (N face of thehexagonal nitride lattice) faces toward the substrate.
 21. The method asclaimed in claim 1, wherein the mirror layer is a Bragg mirror.
 22. Themethod as claimed in claim 1, wherein the mirror has a reflective layerand a radiation-transmissive layer, and wherein theradiation-transmissive layer is between the reflective layer and thesemiconductor layer sequence.
 23. The method as claimed in claim 1,wherein the mirror layer has a reflection layer and a current transportlayer which is different from the reflection layer, and wherein thereflection layer comprises a plurality of windows, the current transportlayer being arranged at least in said plurality of windows and being indirect contact with the semiconductor layer sequence within saidplurality of windows.
 24. A method for micropatterning aradiation-emitting surface of a semiconductor layer sequence for athin-film light-emitting diode chip, comprising the steps of: (a)growing the semiconductor layer sequence on a substrate; (b) forming orapplying a mirror layer on the semiconductor layer sequence, whichreflects back into the semiconductor layer sequence at least part of aradiation that is generated in the semiconductor layer sequence duringoperation thereof; (c) separating the semiconductor layer sequence fromthe substrate with a lift-off method, in which a separation zone in thesemiconductor layer sequence is at least partly decomposed such thatanisotropic residues of a constituent of the separation zone remain at aseparation surface of the semiconductor layer sequence and the substrateis separated from said semiconductor layer sequence, the anisotropicresidues being formed on the semiconductor sequence as a layer having avarying layer thickness; and (d) etching the separation surface—providedwith the anisotropic residues—of the semiconductor layer sequence with adry etching method, a gaseous etchant or a wet-chemical etchant, whereinthe anisotropic residues are temporarily used as an etching mask,wherein the etching results in roughening the separation surface whereinthe separation zone that is decomposed in step (c) contains A1GaN, andAl of said AlGaN of the separation zone is sintered into thesemiconductor layer sequence; and wherein the separation zone has a GaNlayer adjoined by an AlGaN layer on a side remote from the substrate,and in step (c) the entire GaN layer and part of the AlGaN layer aredecomposed.
 25. The method as claimed in claim 24, wherein theanisotropic residues remain after the separation in step (c) on theseparation surface as one of a continuous layer having a varyingthickness and a layer of insular or reticulated zones with interspacesin which a surface of the semiconductor layer sequence has already beenuncovered.
 26. The method as claimed in claim 25, wherein during step(d), the semiconductor layer sequence is etched to different extentsdepending on layer thicknesses of the anisotropic residues to create aroughing of the separation surface of the semiconductor layer sequence.